1. Field of the invention
The invention concerns a centrifugal device for atomizing a coating product such as paint or varnish, for example a product to be applied by electrostatic spraying; it is more particularly concerned with an improvement to the rotating device enabling it to be cleaned quickly and efficiently.
2. Description of the prior art
A known centrifugal device for atomizing a liquid coating product comprises a bowl-shape member rotating at high speed about its main axis of symmetry. The bowl-shape part is joined to a hub by an internal wall generally perpendicular to the rotation axis. This wall divides the interior of the bowl into two cavities: a front cavity open in the spraying direction and a rear cavity surrounding at least the major part of the hub and in which are arranged, fixed and off-axis relative to said rotating member, a coating product nozzle and a cleaning product nozzle. The two nozzles are directed towards the inside surface of the wall. The wall has passages at its outside periphery (usually a series of small diameter holes arranged in a circle) to enable the coating product to flow as the result of centrifugal force along the inside surface of the bowl until it reaches the edge of the latter where it is atomized to form fine droplets. The rotating member is in principle cleaned by spraying the coating product onto the wall, the cleaning product then following the same path as the coating product to the edge of the bowl.
The front surface of the wall is not wetted by the coating product and should therefore remain clean. However, those skilled in the art know that this front surface gradually becomes covered with viscous droplets of coating product, probably because of the extreme air turbulence which occurs in front of the bowl due to its rotation at high speed. These droplets can be propelled by electrostatic forces towards the objects to be coated. They can also be moved by centrifugal force towards the atomizing edge of the bowl, causing large droplets of the coating product to be sprayed onto the object. As a result of this, the deposits on the front surface of the wall eventually cause unacceptable irregularities on the objects to be coated.
Various solutions to this problem have already been put forward. For example, the U.S. Pat. No. 4,275,838 proposes an arrangement in which an external cleaning product nozzle is carried by a mobile member that is retracted during spraying. During cleaning this nozzle is directed towards the front of the bowl. Another proposal (German patent No 30 01 209) is to inject the cleaning product axially at the center of the wall. A further proposal is simply to eliminate the central part and replace it with a divergent hollow frustoconical member at the back of which the cleaning product is injected through a nozzle directed towards the rotating axis. A solution of this kind is described in U.S. Pat. No. 4,684,064, for example. A different proposal is to make the central part of the wall generally convex and to direct onto this part, through passages that converge towards the front, a jet of cleaning product oriented towards the rotation axis. This solution is described in U.S. Pat. No. 4,505,430.
These devices are relatively inefficient and/or characterized by high cost and complexity.
The invention proposes a new type of centrifugal device for atomizing a coating product which is noteworthy because the shape of the rotating member, and specifically the shape of the aforementioned wall, makes it possible to divide the jet of cleaning product into a number of parts flowing in different directions, enabling all surfaces of the bowl to be cleaned, and in particular all of the front surface of the wall.